The present invention relates to a ladle for transferring liquid metal and more particularly to a ladle bottom and a method for using the ladle to eliminate slag so that a higher yield of liquid metal is obtained.
During refinement of molten or liquid metal, such as liquid steel, liquid metal is drained from a ladle, normally through a single outlet hole or outlet nozzle located in the bottom of the ladle, and into an intermediate vessel, called a tundish, or directly into a mold. During this process it is important to completely empty the ladle of metal without the introduction of slag into the tundish or mold. Slag contains undesirable elements which are produced during the refining of liquid metal. Slag floats on the surface of the liquid metal, but during transfer between holding vessels it becomes entrained with the liquid metal. If slag is detected exiting the ladle before the completion of metal drainage, the metal remaining in the ladle is considered lost yield. Therefore it is important to control the amount of slag which is transferred from the ladle to the tundish, or directly to the mold.
A ladle is generally fabricated from steel and lined with refractory materials. The prior art discloses simple refractory hot-face geometries consisting of generally cylindrical refractory sidewalls which include a taper from top to bottom with the bottom diameter being slightly smaller than the top. The term "hot-face" as used herein means the face of the ladle which is in direct contact with the liquid metal in the ladle. Ladle bottoms are normally fashioned from refractory brick or monolithic materials with a flat, stepped, or dish-shaped hot-face geometry.
U.S. Pat. No. 3,695,604 discloses a refractory lining for a sloped floor of a metallurgical vessel having an outlet orifice. The floor is divided into a plurality of sectors and consists of brick and wedge-shaped brick which radiate from the center of the outlet. U.S. Pat. No. 4,079,868 provides dissimilar grooves formed in the sidewalls of a refractory tundish nozzle.
Problems associated with the prior art ladles include slag carry over and entrainment into the liquid metal outlet stream resulting in contamination of the metal in the tundish or mold; the formation of vortexes during drainage which causes the slag to be entrained with the metal in the outlet flow; incomplete metal drainage; and metal penetration into the mortar joints between the bricks and joints and between the bottom and sidewalls.